1. Field of the Invention
This invention relates to a phased array radio frequency pulse generator particularly suitable for producing a plurality of pulsed radio frequency electrical signals.
2. Discussion of Prior Art
In the field of high power radio frequency and microwave generators it is advantageous to be able to operate a plurality of individual sources in a phased array. By the term high power is meant peak powers of at least one MW and preferably as high as peak powers of at least 100 MW. Additionally in this specification the term radio frequency is used to cover radiation in the high frequency, very high frequency, ultra high frequency and microwave regions of the electromagnetic spectrum.
Operating a plurality of individual radio frequency transmitter sources in an array in which the relative phase of radio frequency emission from each element can be controlled is desirable. This allows the generation of high radiation powers at a distance from the phased array source and also allows the formation of a directed beam of radiation. The operation of phased array transmitters is common place at low power levels from each array element such as less than 100 kW but existing radio frequency sources which are used to produce higher power of up to 100 MW or more radio frequency pulses are not operable in phased arrays.
Conventional high power radio frequency and microwave sources are magnetrons, klystrons and travelling wave tubes (TWT's). Generally these devices operate by generating a beam of electrons which passes through a period mechanical structure. The electron beam interacts with the mechanical structure and energy is extracted from the electron beam to produce a radio frequency or microwave field inside the mechanical structure which is typically a cavity. Radio frequency or microwave energy is then extracted from the cavity as required. Radar transmitters have utilised electron beam/resonant cavity devices of this kind and phased arrays have been developed which use these devices. Conventionally beam formation in an array of radio frequency transmitter elements is controlled by phased scanning and time delay scanning.
Conventionally phase scanning phase shifters are incorporated at the output of each radio frequency modulator element with the phase shifters being electronically actuated to control the phase excitation of each of the radiating elements. Conventional phase shifters are usually based on diodes or on ferrite components. The power handling capacity of such diode phase shifters is generally limited to about 1 kW peak power and the power handling capacity of conventional ferrite phase shifters is limited to about 100 kW peak power.
In the case of time delay scanning conventionally incremental delays are introduced between each radio frequency modulator and the corresponding radiating element. These delays may be introduced by including switched delay lines or switched circulators but however introduced these conventional electronically controlled delay devices are also limited in power handling capacity to approximately 100 kW peak power.
There is thus a need for a generally improved phased array radio frequency pulse generator which will allow for electronic control of the relative phase of the parts therein which produce high peak power radio frequency pulses, for example with peak powers of 100 MW or higher.